1. Field of the Invention
The present invention relates to a coating method for a glass vacuum flask and the devices for performing such a coating method, which is easy and inexpensive to perform and does not produce pollution.
2. Description of the Prior Art
The vacuum flask may be made from glass or metal material. The glass vacuum flask consists of an inner flask and an outer flask. The inner and outer flasks are incorporated into a double-layer container with a gap defined therebetween. The outer surface of the inner flask and the inner surface of the outer flask are respectively coated with a layer of silver and incorporated with each other into a unitary reflecting surface. After coating, the air in the gap between the inner and outer flasks is exhausted, and therefore, the gap is formed into a vacuum chamber. Because glass material provides low heat conductivity, the reflecting surface can reflect radiation of heat, and the vacuum chamber can reduce the effect of heat conviction to the minimum. Therefore, a glass vacuum flask of this kind can be used for keeping liquids hot (or cold) for a long time.
FIG. 1 is a flow chart of the prior art glass vacuum flask manufacturing process. A blank for inner flask (A.sub.0) is obtained through the process of blowing (Step I). The blank for inner flask (A.sub.0) is treated through cutting and flaring processes to form into an inner flask (A) by cutting off the cullet (A.sub.2) thereof and forming a flare (A.sub.1) thereof, and then, the bottom of the inner flask (A) is adhered with an asbestos cushion (A.sub.3) (Step II). During the formation of the inner flask (A), a blank for outer flask (B.sub.0) is obtained through the process of blowing (Step III) and then, treated through tubulating process (Step IV). During the tubulating process (Step IV), a glass tube (B.sub.1) is welded to the bottom edge of the blank of the outer flask (B.sub.0) to connect the inner space between the blanks with outer space. The blank for outer flask (B.sub.0) is covered over the inner flask (A) and treated by rollers (not shown) through heat rolling process to shrink into a shape to fit the inner flask (A) (see the dotted line in Step V), and then, the cullet (B2) of the blank of outer flask (B.sub.0) is cut off, and therefore, an outer flask (B) is formed with the inner flask (A) maintained therein. The openings of the inner flask (A) and the outer flask (B) are then sealed through the process of neck sealing annealing (Step VI). Then, tin dichloride solution is filled through the glass tube (B.sub.1) into the gap (G) between the inner and outer flasks (A, B) to activate the glass surface for further silvering process (Step VII). During silvering process, silver nitrate solution and formalin or suitable reducing agent are filled into the gap (G) to form a silver coating over the glass surface inside the gap (G). After washing, the silver coated flask is treated through stoving process (Step VIII) to remove moisture from the silvering process. The flask is further treated through exhausting process to a vacuum status below 1.times.10.sup.-3 Torr and then treated through tipping off process (Step IX). After Step IX, the flask is then treated through temperature testing (Step X). After approval through temperature testing, a flask is finished.
The aforesaid prior art of vacuum flask manufacturing process is complicated to achieve. The materials used for silver coating are expensive. The use of tin dichloride, silver nitrate and reducing agent will produce poisonous waste water which may cause serious environmental pollution. In order to treat the waste water from the manufacturing process, expensive waste water treating equipment shall be required. Further, any residual silver solution in the gap between the inner and outer flasks may affect the performance of vacuum process. In addition to the aforesaid disadvantages, the aforesaid prior art of vacuum flask manufacturing process requires experienced workers to operate. Since only experienced workers can do the job, the manufacturing cost of a glass vacuum flask according to the aforesaid process is therefore increased.